Air cycle heating or cooling

ABSTRACT

A method and apparatus for pumping heat utilizes air or other gas as the working fluid wherein a positive displacement compressor and a positive displacement expander are mechanically interlocked, the swept volume per unit time of the compressor relative to the swept volume per unit time of the expander being a function of absolute temperature of the air drawn into the compressor relative to the absolute temperature of the air provided for the expander. A heat exchanger is positioned between and connecting the compressor exhaust and the expander intake to purge heat from the compressed air flowing therethrough, the compressed air being released to ambient pressure through the expander to extract work from the air concurrent with cooling of the air through expansion and apply the extracted work to the compressor through the mechanical interlinking between the expander and the compressor, and means to provide supplemental heat when utilizing the heat pump to provide heat.

United States Patent Huntley July 29, 1975 AIR CYCLE HEATING OR COOLINGPrimary Examiner-William J. Wye [76] Inventor: Leslie E. Huntley, Rt. 1,PO. Box 7,

Reubens, Idaho 83548 ABSTRACT [22] Filed: Feb. 11, 1974 A method andapparatus for pumping heat utilizes air [2]} Appl. No.: 441,406

or other gas as the working fluid wherein a positive displacementcompressor and a positive displacement expander are mechanicallyinterlocked, the swept volume per unit time of the compressor relativeto the swept volume per unit time of the expander being a function ofabsolute temperature of the air drawn into the compressor relative tothe absolute temperature of the air provided for the expander. A heatexchanger is positioned between and connecting the compressor exhaustand the expander intake to purge heat from the compressed air flowingtherethrough, the compressed air being released to ambient pressurethrough the expander to extract work from the air concurrent withcooling of the air through expansion and apply the extracted work to thecompressor through the mechanical interlinking between the expander andthe compressor, and means to provide supplemental heat when utilizingthe heat pump to provide heat.

12 Claims, 5 Drawing Figures PATENTEU JUL 2 9 i975 AIR CYCLE HEATING ORCOOLING The present invention relates generally to heating- /coolingsystems, and more particularly to heat pumping devices using air, gas orother working fluids which are adaptable for selective heating orcooling of a defined enclosed environment.

The desirability of providing air or gas at a temperature either aboveor below that of ambient temperature has long been recognized. Commonly,the provision of air at a temperature below the ambient temperature isprovided by heat pumping wherein the heat extracted from the cooled airis exhausted outside of the enclosed environment. Liquid-vapor systemsare commonly utilized to accomplish this. In such systems, the workingfluid in vapor form is compressed to form a liquid at a relativelyelevated temperature, the heat from the working fluid is transferred toanother fluid and conducted outside of the enclosed environment, and thethus cooled liquid is then expanded to a lower pressure therebyproviding a vapor at a much lower temperature which, in turn, is warmedthrough heat exchange with air conducted to the enclosed environment.Obviously, this process is reversible and the heat may be pumped to theinterior rather than the exterior of the subject enclosed environment.

Instead of utilizing the conventional closed circuit liquid-vaporworking fluid, air may be directly utilized as a working fluid andsubjected to a roughly analogous process, i.e., compression to heat theworking fluid, heat exchange to cool the compressed working fluid andexpansion to lower pressure and temperature. There are certainsimplifications, cost savings and safety factors to be gained throughthe use of air as a working fluid. For instance, the closed systemsliquidvapor cycle requires a heat exchange step between the cooled vaporand air provided to the enclosed environment wherein a system utilizingair as the working fluid can directly exhaust the cooled air to theenclosed environment. No toxic working fluids are employed in air cycleapparatus. This provides an obvious safety factor while concurrentlyminimizing maintenance.

An example of an advanced system utilizing air as the working fluid isto be found in United States letters Patent No. 2,496,602. This patentdiscloses the use of turbine-type compressors and expanders, the twobeing linked to extract work from the expansion and apply it to thecompressor. However, since the expansion and compression steps are mostefficiently conducted in an adiabatic manner, and since the turbinesinherently compromise adiabatic compression and expansion, certaindrawbacks exist with regard to this prior art system. Also, turbinestend to be inefficient at modest flow rates.

Other prior art references, which are believed to be less pertinent thanthe above-discussed patent, include United States letters Patent Nos.1,966,938, 2,586,002, 2,971,343, and 3,623,332.

The present invention which provides heretofore unavailable improvementsin efficiency, simplicity and versatility over previous air workingfluid heat pumps, comprises a method and device for reversibly providingeither heated or cooled air in a simplified and efficient manner. Themethod and apparatus utilizes positive displacement compressor andexpander components, such as piston and cylinder arrangements, vanepumps such as the Roots, or Pappenheim devices, or other similar oranalogous positive displacement rotary,

swash plate or reciprocating pumps and motors. After air is brought toan elevated pressure by the compressor and, accordingly, the temperatureraised appreciably, the air is conducted through a heat exchanger towithdraw heat therefrom. Because of the relatively elevated-temperatureof the compressed air, it is not difficult to maintain the temperaturedifferential necessary for such heat exchange, since even the ambienttemperatures will be at a substantially lower temperature than thecompressed air. Preferably, the heat exchange is concurrent with exhaustair from the subject enclosed environment providing the lowertemperature medium.

After cooling, the compressed air is expanded through the expander whichextracts work therefrom. Expansion concurrently induces a marked coolingof the air as it returns to ambient pressure. The expanded workingmedium then may be exhausted directly into the enclosed environment.Alternatively, as will be discussed below, the heat extracted from thecompressed air by heat exchange can be directed into the enclosedenvironment.

To enhance efficiency, the work extracted by expansion of the compressedair through the expander is mechanically applied to the compressor. Thisgreatly alleviates the necessity for energy to be supplied to thesystem, although, of course, the work available from the expander is notalone adequate to operate the compresv sor. Accordingly, additionalenergy is supplied either directly to the compressor, or, as will bedescribed below, through an auxiliary compressor.

In the event heating is desired, the relationship between the compressorand expander may be reversed, i.e., with the gas exhausted through theexpander being vented to the exterior and the heat exchange medium towhich heat is transferred from the compressed air being directed to theenclosed environment. Since the efficiency of providing heated air, asopposed to cooled air, may be less depending upon the heating rangerequired and thus require a more substantial apparatus, it is often moreadvantageous to provide additional heat directly into the hot air outputrather than to size the apparatus for heating while providing greatlyexcess capacity for cooling.

Also, heat may be provided while the apparatus is operated in a coolingmode but with the exhaust air being heated substantially beforebeingconducted through the heat exchanger in order that heat is transferredto the compressed" air rather than extracted therefrom. In thissituation, upon expansion, the air will not be cooled below the ambienttemperature but instead will be warmer than the air introduced into thecompressor. This approach has the advantage of having substantial poweravailable through the expander which may be utilized to run auxiliaryequipment in addition to the compressor.

Accordingly, an object of the present invention is to provide a new andimproved method and apparatus for pumping'heat using air as the workingmedium with substantially adiabatic compression and expansion.

Another object of the-present invention is to provide a new and improvedmethod and apparatus for pumping heat utilizing air as the workingmedium which is readily reversible from a cooling to a heating mode.

Yet another object of the present invention is to provide a new andimproved method and apparatus for providing air cycle heat pumpingwherein the compressor and expander drives are mechanically connectedwhereby the expander functions as a motor and provides an auxiliarydrive to the compressor.

Still another object of the present invention is to provide a device ofthe above-described nature wherein the pumping capacities of thecompressor and the expander are sized to provide high efficiency withoptimum compression of the working medium.

These and other objects and features of the present invention willbecome apparent from the following description.

FIG. 1 is a simplified, partially-sectioned illustration of anembodiment of the present invention;

FIG. 2 is a simplified, partially-sectioned illustration of anotherembodiment of the present invention.

FIG. 3 is a simplified, partially-sectioned illustration of yet anotherembodiment of the instant invention; and

FIGS. 4 and 5 are simplified, partially-sectioned illustrations ofembodiments of the instant invention particularly adapted for generatingsubstantial amounts of heat.

Turning now to the drawings, wherein like components are designated bylike reference numerals throughout the various figures, a device forpumping heat utilizing an air cycle is illustrated in FIG. 1 andgenerally designated by reference numeral 10. Heat pump includespositive displacement compressor 12 and positive displacement expander13. A typical posifive-displacement compressor 12 is comprised, asillustrated, of cylinder 15 having piston 16 sealingly and slidinglydisposed therein. Connecting rod 17 is pivotally attached to piston 16.Intake valve 18 and exhaust valve 19 are positioned in cylinder head 20at an upper portion of cylinder 15. Intake valve 18 and exhaust valve 19may be flap or reed valves actuated by pressure difference, or, forinstance, poppet valves positively operated by cams (not shown) in aconventional synchronized manner.

Compressor 12 operates on a two-stroke cycle with intake valve 18 openas piston 16 moves downward and, exhaust valve 19 selectively advancedto an open position as piston 16 moves upward. Accordingly, air is drawninto cylinder 15 through intake valve 18 as piston 16 moves downward andexpelled therefrom through exhaust valve 19 as piston 16 moves upward.

Expander 13 is, as illustrated, similar to compressor 12 inconstruction. Expander cylinder 21 contains piston 22 sealingly andslidingly disposed therein. Connecting rod 23 is pivotally attached topiston 22. Intake valve 24 and exhaust valve 25, which are positivelyactuated by means not shown, are disposed in the cylinder head at theupper end of cylinder 21.

Since heat pump 10 operates to provide heated or cooled air to theinterior of an enclosed environment, wall 27 is schematically indicatedto establish such inner and outer relationship. Dependent upon operationof heat pump 10 in a cooling or in a heating function, differing sidesof wall 27 may be considered as being the enclosed environment.Compressor l2 and expander 13 are in communication through wall 27 bymeans of heat exchanger 28, and, more specifically, by means ofpressurized passage 29 of heat exchanger 28. Pressurized passage 29 isin communication with exhaust valve 19 of compressor 12 and intake valve24 of expander 13. Further, pressurized passage 29 is sealed fromexhaust passage 30 but includes a substantial wall area in common toprovide a heat exchange relationship between the air in pressure passage29 and cooler air in exhaust passage 30.

Connecting rod 17 of compressor 12 is connected in an eccentric mannerto compressor pulley 32. Connecting rod 23 of expander 13 is connectedin the same manner to variable diameter expander pulley 33. It will benoted that expander pulley 33 may vary in diameter from that ofcompressor pulley 32, the ratio of pulley diameters being approximatelyequal to the ratio of temperatures, and for instance one or both pulleys32 and 33 may be variable pitch V-belt pulleys. Another motor-drivenpulley 34 is connected to both compressor pulley 32 and expander 33 bymeans of belt 35. Accordingly, as a result of the difference in thediameters of compressor pulley 32 and expander pulley 33, the rate atwhich compressor 32 pumps a given volume of air will differ from therate at which expander 13 permits the volume of air to be exhausted.This relationship is necessary since a given mass of air occupiesdiffering volumes as pressure and temperature change. More specifically,the volume varies inversely proportional to changes in the absolutepressure and directly proportional to changes in the absolutetemperature. As a result, the air ingested into compressor 12 isdetermined by the swept volume, or effective swept volume, of compressor12 and the temperature and pressure of the air at intake valve 18.Similarly, the volume of air used to drive expander 13 is determined bythe temperature and pressure of the air at intake valve 24. Since theair in pressurized passage 29 of exchanger 28 is, in general, at ahigher pressure and temperature than the ambient air, these offsettingfactors must be taken into account in sizing expander 13. Further, theeffective swept volume of expander 13 may be less than the displacementthereof since it may be desirable to close intake valve 24 before piston22 reaches bottom deadcenter. Obviously, if intake valve 24 were in theopen position when piston 22 is at bottom dead-center, the pressureswithin cylinder 21 would be the same as that within pressurized passage29 and this pressure would, upon the opening of exhaust valve 25, ventto ambient pressure without doing reclaimable work. For this reason,closure of intake valve 24 before piston 22 reaches bottom dead-centerestablishes an effective swept volume and the pressure in cylinder 21will be rather closer to ambient temperature upon opening of exhaustvalve 25.

In order to compensate for the different volumes passing throughcompressor 12 and expander 13 as a result of differing temperatures, thesize of compressor pulley 32 and expander pulley 33 differ. Further,once the apparatus has reached a steady-state operation, the pressure inpassage 29 may be monitored and maintained at a predetermined optimumvalue. For instance, pressure sensor 38 within pressure passage 29 ofheat exchanger 28, in conjunction with controller 39, produces an outputsignal which varies the diameter of, for instance. expander pulley 33 tomaintain the pressure at the desired level. When the pressure exceedsthe desired value. the diameter of expander pulley 33 decreases therebyincreasing the swept volume per unit time of expander 13. The converseoccurs when the pressure is below the desired level.

Another variant of the same general type of apparatus is illustrated inFIG. 2 wherein the diameters of compressor cylinder 15 and expandercylinder 21 differ. Accordingly, though piston 16 of compressor 12 andpiston 22 of expander 13 may move linearly at identical rates. the sweptvolume per unit time will, of course, vary as the square of thediameters. Piston 16 is rigidly attached to piston 22 by means of linkmember 44 which extends sealingly through compressor cylinder head 42and expander cylinder head 43. Expander piston 22 is connectedeccentrically to crank shaft 45 by means of connecting rod 23. Crankshaft 45, in turn, is driven by motor 46. Accordingly, rotation of crankshaft 45 moves piston 22 reciprocally in cylinder 21 and, in unison,also moves piston 16 and cylinder by means of link member 44. Since thediameters of compressor cylinder 15 and expander cylinder 21 cannot bevaried during operation, the sizes thereof are determined forsteady-state operating conditions.

An apparatus somewhat similar to that of FIG. 2 is illustrated in FIG.3. Expander piston 22, which is of a diameter identical to that ofcompressor piston 16, is linked to undriven flywheel 48 by connectingrod 23. Energy is supplied to the system by auxiliary compressor 49which provides compressed air to pressurized passage 29. In order toinitiate and maintain move ment, auxiliary expander cylinder 50 withauxiliary expander piston 51 disposed therein is linked throughauxiliary expander linkage 52 to link member 44. Since auxiliaryexpander piston 51 is in communication with pressurized passage 29, aforce imbalance is exerted upon the combined expander end of the systemand causes movement of the linked auxiliary expander piston 51, expanderpiston 22 and compressor piston 16.

As with any of the embodiments of the instant invention, it is to beunderstood that the apparatus may be run in a reversed configurationwith the illustrated expander functioning as a compressor and theillustrated compressor functioning as an expander. Thus, a fullybalanced system would have auxiliary expanders being selectively engagedand disengaged depending upon the desired mode of operation.

An example of an apparatus run in the reversed or heating mode isschematically illustrated in FIG. 4 wherein compressor 12 is consideredto be within the enclosed environment and expander 13 outside of theenclosed environment. Therefore, the air exiting from exhaust passage 30will be heated as a result of heat exchange between the compressed airin pressure passage 29 and the lower temperature air drawn into exhaustpassage 30 from outside the environment. However, since the air drawninto exhaust passage 30 is often quite cool in instances requiringoperation in the heating mode, the apparatus operates in a lessefficient manner. and in the case of extreme heating ranges would begreatly oversized for the normal cooling demand. For this reason, anauxiliary heating element 55 is provided in heat exchanger passage 30 tofurther heat the air provided to the enclosed environment.

Still another embodiment is shown in FIG. 5 wherein compressor 12 andexpander 13 are operated in the cooling" mode, but a burner 58 isprovided to heat the air through exhaust passage 30. Thus, the air inexhaust passage 30 will be at an elevated temperature and transfer heatinto the air in pressure passage 29, even though the compressed air inpressurized passage 29 is heated to a substantial degree by compressionto a higher level. For this reason, the air is exhausted from pressurepassage 29 through expander 13 and will be heated above ambienttemperature even though substantial amounts of work may be provided toauxiliary power unit 60 by expander 13.

Summarily, it will be seen that the present invention, as described andillustrated, provides an efficient manner for providing either heated orcooled air. By using positive displacement compressors and expanders,and by utilizing the power produced by exhausting the compressed airthrough the expander to drive, at least in part, the compressor,efficiency is substantially enhanced and the requirement for acomplicated closed system and toxic working fluid is avoided. Theadditional power required can be provided by a motor driving thecompressor, by an auxiliary driven compressor or by heat added to thesystem. In these latter two cases, the expanders may function to drivethe compressor without an additional motor drive to the compressor.

Although several embodiments of the present invention have beenillustrated and described, it is anticipated that various changes andmodifications beyond the illustrated embodiments will be apparent tothose skilled in the art and that such changes may be made withoutdeparting from the scope of the invention, as defined by the followingclaims.

What is claimed is:

1. A method for transferring heat between a first environment and asecond environment, comprising: substantially adiabatically compressinggaseous working medium from the first environment by means of a positivedisplacement compressor, conducting the compressed and, accordingly,heated gaseous working medium from the compressor through a pressurepassage of a heat exchanger to a positive displacement expander,conducting exhaust gaseous working medium from the second environmentthrough a second passage of the heat exchanger to the first environment,transferring heat from the heated, compressed gaseous working medium tothe exhaust gaseous working medium, adiabatically expanding thecompressed gaseous working medium from which heat has been transferredthrough the positive displacement expander and into the secondenvironment to extract work. from and cool the expanded gaseous workingmedium, applying the work obtained from the expansion of the compressedgaseous working medium from the expander to the compressor, and varyingthe ratio of the effective swept volume per unit time of the compressorrelative to the effective swept volume per unit time of the expanderdirectly as the absolute temperature of the first environment varies,whereby cool gaseous working medium is provided from the expander to thesecond environment, heated exhaust gaseous working medium is suppliedfrom the heat exchanger to the first environment and energy is conservedby the application of work from the expander to the compressor and bythe substantially adiabatic compression and expansion of the compressedgaseous working medium.

2. A method as set forth in claim 1 wherein the ratio of the effectiveswept volume per unit time of the compressor and the effective sweptvolume per unit time of the expander is maintained at a predeterminedvalue at a predetermined operational pressure of the compressed gaseousworking medium in the heat exchanger and increased when the pressure ofthe compressed gaseous working medium in the heat exchanger falls belowthe predetermined value and decreased as the pressure of the compressedgaseous working medium of the heat exchanger exceeds the predeterminedvalue.

3. A method as set forth in claim 1 wherein heat is added to the exhaustair in the heat exchanger before heat exchange between the exhaustgaseous working medium and the compressed gaseous working medium, and inwhich the gaseous working medium exhausted from the expander is at atemperature higher than the ambient temperature in the firstenvironment.

4. A method as set forth in claim 1 wherein heat is added to the exhaustgaseous working medium in the heat exchanger after heat exchange of suchgaseous working medium with the compressed gaseous working medium andthe quantity of heat supplied to the first environment by the exhaustgaseous working medium is accordingly increased.

5. Apparatus for transferring heat between a first environment and asecond environment, comprising: means separating the first environmentfrom the second environment, a positive displacement compressoringesting a gaseous working medium from the first environment, a heatexchanger having at least two passages defined therethrough, one of theheat exchanger passages comprising a pressure passage communicating withthe exhaust port of the compressor at one end and with an intake port ofa positive displacement expander at the other end thereof, the otherpassage of the heat exchanger being in a heat-exchange relationship withthe pressure passage and communicating with the first environment at oneend and the second environment at the other end, means interlinking thecompressor and expander for transferring work between the drive of theexpander and the drive of the compressor, means for applying energy tosaid compressor and said expander, and means for controlling said energyapplying means for varying the ratio of the effective swept volume perunit of time of said compressor to the effective swept volume per unitof time of said expander.

6. An apparatus as set forth in claim 5 wherein the means interlinkingthe expander and compressor is a belt, the means for supplying energy tothe apparatus is a drive motor bearing upon the belt by means of apulley, and said controlling means includes a variable diameter ratiopulley whereby the relative operating speeds of the compressor and theexpander can be var ied.

7. An apparatus as set forth in claim 6 wherein a pressure sensor isprovided in the pressure passage and includes means to vary the diameterof the variable diameter pulley in response to changes in pressurewithin the pressure passage.

8. An apparatus as set forth in claim 5 wherein a heat-producing meansis positioned within one of the heat exchange passages between the firstand second environment at a position adjacent the second environment.

9. An apparatus as set forth in claim 5 wherein a heat-producing meansis positioned within one of the heat exchange passages between the firstand second environment at a position adjacent the first environment.

10. Apparatus for transferring heat between a first environment and asecond environment comprising: means separating the first environmentfrom the second environment, a positive displacement compressoringesting a gaseous working medium from the first environment and havinga piston mechanism, a positive displacement expander having a pistonmechanism of an effective working surface greater than that of saidcompressor piston, a heat exchanger having at least two passages definedtherethrough, one of said passages being a pressure passagecommunicating with the exhaust port of said compressor and the intakeport of said expander, the other said passage being in heatexchangerelationship with the said pressure passage and communicating betweenthe first and second environments, means interlinking said compressorand expander pistons, and means for introducing pressure into saidpressure passage, whereby the said compressor piston will drive theapparatus and work will be transferred between said compressor andexpander via said interlinking means.

11. An apparatus as set forth in claim 10 wherein the compressor andexpander each have piston devices of the same diameter, the interlinkingmeans is a link rod commonly attached to the piston in the compressorand the piston in the expander, said introducing means includes anauxiliary-driven compressor communicating with the pressure passage ofthe heat exchanger, and said compressor also includes an auxiliaryexpander of a piston device type attached by means of an auxiliarylinkage between the auxiliary expander piston and the link rod to boththe expander and compressor.

12. Apparatus in accordance with claim 11 wherein the intake and exhaustports for said auxiliary expander piston both communicate with saidpressure passage.

1. A method for transferring heat between a first environment and asecond environment, comprising: substantially adiabatically compressinggaseous working medium from the first environment by means of a positivedisplacement compressor, conducting the compressed and, accordingly,heated gaseous working medium from the compressor through a pressurepassage of a heat exchanger to a positive displacement expander,conducting exhaust gaseous working medium from the second environmentthrough a second passage of the heat exchanger to the first environment,transferring heat from the heated, compressed gaseous working medium tothe exhaust gaseous working medium, adiabatically expanding thecompressed gaseous working medium from which heat has been transferredthrough the positive displacement expander and into the secondenvironment to extract work from and cool the expanded gaseous workingmedium, applying the work obtained from the expansion of the compressedgaseous working medium from the expander to the compressor, and varyingthe ratio of the effective swept volume per unit time of the compressorrelative to the effective swept volume per unit time of the expanderdirectly as the absolute temperature of the first environment varies,whereby cool gaseous working medium is provided from the expander to thesecond environment, heated exhaust gaseous working medium is suppliedfrom the heat exchanger to the first environment and energy is conservedby the application of work from the expander to the compressor and bythe substantially adiabatic compression and expansion of the compressedgaseous working medium.
 2. A method as set forth in claim 1 wherein theratio of the effective swept volume per unit time of the compressor andthe effective swept volume per unit time of the expander is maintainedat a predetermined value at a predetermined operational pressure of thecompressed gaseous working medium in the heat exchanger and increasedwhen the pressure of the compressed gaseous working medium in the heatexchanger falls below the predetermined value and decreased as thepressure of the compressed gaseous working medium of the heat exchangerexceeds the predetermined value.
 3. A method as set forth in claim 1wherein heat is added to the exhaust air in the heat exchanger beforeheat exchange between the exhaust gaseous working medium and thecompressed gaseous working medium, and in which the gaseous workingmedium exhausted from the expander is at a temperature higher than theambient temperature in the first environment.
 4. A method as set forthin claim 1 wherein heat is added to the exhaust gaseous working mediumin the heat exchanger after heat exchange of such gaseous working mediumwith the compressed gaseous working medium and the quantity of heatsupplied to the first environment by the exhaust gaseous working mediumis accordingly increased.
 5. Apparatus for transferring heat between afirst environment and a second environment, comprising: means separatingthe first environment from the second environment, a positivedisplacement compressor ingesting a gaseous working medium from thefirst environment, a heat exchanger having at least two passages definedtherethrough, one of the heat exchanger passages comprising a pressurepassage communicating with the exhaust port of the compressor at one endand with an intake port of a positive displacement expander at the otherend thereof, the other passage of the heat exchanger being in aheat-exchange relationship with the pressure passage and communicatingwith the first environment at one end and the second environment at theother end, means interlinking the compressor and expander fortransferring work between the drive of the expander and the drive of thecompressor, means for applying energy to said compreSsor and saidexpander, and means for controlling said energy applying means forvarying the ratio of the effective swept volume per unit of time of saidcompressor to the effective swept volume per unit of time of saidexpander.
 6. An apparatus as set forth in claim 5 wherein the meansinterlinking the expander and compressor is a belt, the means forsupplying energy to the apparatus is a drive motor bearing upon the beltby means of a pulley, and said controlling means includes a variablediameter ratio pulley whereby the relative operating speeds of thecompressor and the expander can be varied.
 7. An apparatus as set forthin claim 6 wherein a pressure sensor is provided in the pressure passageand includes means to vary the diameter of the variable diameter pulleyin response to changes in pressure within the pressure passage.
 8. Anapparatus as set forth in claim 5 wherein a heat-producing means ispositioned within one of the heat exchange passages between the firstand second environment at a position adjacent the second environment. 9.An apparatus as set forth in claim 5 wherein a heat-producing means ispositioned within one of the heat exchange passages between the firstand second environment at a position adjacent the first environment. 10.Apparatus for transferring heat between a first environment and a secondenvironment comprising: means separating the first environment from thesecond environment, a positive displacement compressor ingesting agaseous working medium from the first environment and having a pistonmechanism, a positive displacement expander having a piston mechanism ofan effective working surface greater than that of said compressorpiston, a heat exchanger having at least two passages definedtherethrough, one of said passages being a pressure passagecommunicating with the exhaust port of said compressor and the intakeport of said expander, the other said passage being in heat-exchangerelationship with the said pressure passage and communicating betweenthe first and second environments, means interlinking said compressorand expander pistons, and means for introducing pressure into saidpressure passage, whereby the said compressor piston will drive theapparatus and work will be transferred between said compressor andexpander via said interlinking means.
 11. An apparatus as set forth inclaim 10 wherein the compressor and expander each have piston devices ofthe same diameter, the interlinking means is a link rod commonlyattached to the piston in the compressor and the piston in the expander,said introducing means includes an auxiliary-driven compressorcommunicating with the pressure passage of the heat exchanger, and saidcompressor also includes an auxiliary expander of a piston device typeattached by means of an auxiliary linkage between the auxiliary expanderpiston and the link rod to both the expander and compressor. 12.Apparatus in accordance with claim 11 wherein the intake and exhaustports for said auxiliary expander piston both communicate with saidpressure passage.